POwer test of 4Pole Mission

Well done solving the problem. I’d consider replacing the regulators eventually as being reverse biassed can shorten their life (found that out from my Oberheim Cyclone that had no reverse voltage protection for plugpacks!)

You advice me to replace them ? if I understand

They cost very little, so for peace of mind it can be worth it.

Argh! I am also having power test problems now. I’m using a 12-volt power supply, 500ma, that’s putting out 17v at SW. The readings at the indicated coloured dots, with the LT1054 (IC7) in are minimal, .06v, and are reversed polarity. I checked the polarity of the polarized caps and they seem to be in the right place, and I assumed the long lead of the 4.7u caps was positive. The regulators are installed with the heatsinks facing the outside of the PCB.

Any ideas? Someday, maybe when I do my 20th Shruthi, I’ll actually get one to work first time.

Randy

17v might be to much. LT1054 datasheet says “Operating Range: 3.5V to 15V”

i have no idea what happens at > 15v, but i figure using another psu with like 7,5 - 12v might be something to try

Looks like you have fried the LT1054.

Always be cautious with supplying power. Too little is better than too much. With too little it just won’t switch on.

I may have fried the chip. Is there a way to test it?

The first power supply I tried, also rated at 12V put out nearly 20V! I’ll see if I can find another LT1054.

Randy

If you don’t get minus the input voltage on pin 5 of the LT1054 it’s dead. This seems consistent with your observations. The LT1054 is not designed to handle voltages above 15V so there’s not much hope here…

At least I’ve learned to ignore whatever is written on the wallwarts and test them first.

Randy

It’s not just about testing them. But realising that a good many of them put out a higher voltage when they are unloaded. Or will put out a higher voltage when their amperage rating is far in excess of what the Shruthi actually needs, as they are not loaded enough for the voltage to settle down to where it should be.
In my experience, switchable wallwarts are often crappy about putting out what they are supposed to be putting out too.

I guess a regulated wallwart would help, but there isn’t really much need. Suitable, unregulated ones are cheap and generally easy to get hold of.
I don’t think the Shruthi requires more than 300ma(??). I have 9v 500ma and 660ma ones from RS and Farnell and they have been fine with all my Shruthi’s so far.

The Shruthi doesn’t need more than 150mA. The problem is that it’s common to see wallwarts rated 300mA fail to deliver the 150 or 160 the Shruthi needs :confused:

Godlyke Powerall and be done with it! It makes all my Shruths work (at the same time). MidiPal too.

I picked up another (well, a pair, just in case) LT1054 and tested with the power supply I’m using for the other Shruthi, same result. Minimal power getting through to anything.

I checked all of the caps again and they seem to be oriented correctly. The only thing I’m not sure of is the orientation of the 4.5u caps that Olivier provides with the kit. As I mentioned, I assumed the long lead was positive, but I can’t see any markings on those caps that would let me check the orientation after-the-fact.

So, I’m back to looking for ideas.

Randy

These caps are not polarized, so no worry here.

Do you have a short between ground and one of the +5V or -5V rails?

Which voltage do you get at pin 5 of the LT1054?

I used pin 3 as ground and I’m getting +0.2v at pin 5. All of the red points on the photo are getting +0.4v and all of the blue are +0.3v.

I checked continuity between all of the green, red and blue points and everything seems okay. The odd one has the meter “hunting” a bit but it settles down to 1 quickly.

Randy

What are the voltages on both sides of D1?

Depends on which probe I use. I have 15.3 at SW, then if I leave the + on SW, I get 15 on both sides of D1. If I leave the - on SW, I get essentially nothing on both sides.

When measuring a voltage the (-) should always be put on a ground point ; and the (+) on the point you want to measure the voltage at. Otherwise you are measuring voltage differences.

What is the best point to get a ground?